Do you need a separate bill of sale?
Usually not — the title carries the price
The assignment on the title does the work when it has a space for the purchase price. If it does not, Kansas requires a bill of sale, page 2 of form TR-12. A useful Kansas option instead: the seller may complete a Power of Attorney, form TR-41, allowing the buyer to complete the assignment. If the title came from another state, or the bill of sale is from an out-of-state owner, the vehicle must be inspected before Kansas will title it. For a gift, complete the Vehicle Gift Certification on form TR-12 and write “gift” in the price space on the title.
Source: Kansas DOR, Titling a used vehicle; Kansas DOR, Title FAQ; forms TR-41 and TR-12